Hearing aid with improved localization

ABSTRACT

A method of determining parameters of a BTE hearing aid having at least one ITE microphone and at least one BTE microphone, the method includes: determining Head-Related Transfer functions HRTF l (ƒ); determining a hearing aid related transfer function H l,i   ITEC (ƒ) of a i th  microphone of the at least one ITE microphone for direction l; determining a hearing aid related transfer functions H l,j   BTEC (ƒ) of a j th  microphone of the at least one BTE microphone; determining transfer functions G i   IEC (ƒ) of a i th  cue filter of at least one cue filter filtering audio sound signals of the at least one ITE microphone; and determining transfer functions G j   BTEC (ƒ) of a j th  cue filter of the at least one cue filter filtering audio sound signals of the at least one BTE microphone; wherein the transfer functions G i   IEC (ƒ) and the transfer functions G j   BTEC (ƒ) are determined using a processing unit based on equation:
 
min G     i       IEC     (ƒ),G     i       BTEC     (ƒ) Σ l=0   L-1   W ( l )∥ W (ƒ)HRTF l (ƒ)−Σ i   G   i   IEC (ƒ) H   l,i   IEC (ƒ)−Σ j   G   j   BTEC (ƒ) H   l,j   BTEC (ƒ))∥ p .

RELATED APPLICATION DATA

This application claims priority to and the benefit of Danish PatentApplication No. PA 2012 70832, filed on Dec. 28, 2012, and EuropeanPatent Application No. 12199720.9, filed on Dec. 28, 2012. Thedisclosures of all of the above applications are expressly incorporatedby reference in their entireties herein.

FIELD

A new hearing aid is provided with improved localization of soundsources with relation to the wearer of the hearing aid.

BACKGROUND

Hearing aid users have been reported to have poorer ability to localizesound sources when wearing their hearing aids than without their hearingaids. This represents a serious problem for the mild-to-moderate hearingimpaired population.

Furthermore, hearing aids typically reproduce sound in such a way thatthe user perceives sound sources to be localized inside the head. Thesound is said to be internalized rather than being externalized. Acommon complaint for hearing aid users when referring to the “hearingspeech in noise problem” is that it is very hard to follow anything thatis being said even though the signal to noise ratio (SNR) should besufficient to provide the required speech intelligibility. A significantcontributor to this fact is that the hearing aid reproduces aninternalized sound field. This adds to the cognitive loading of thehearing aid user and may result in listening fatigue and ultimately thatthe user removes the hearing aid(s).

Thus, there is a need for a new hearing aid with improved localizationof sound sources, i.e. the new hearing aid preserves information of thedirections and distances of respective sound sources in the soundenvironment with relation to the orientation of the head of the wearerof the hearing aid.

Human beings detect and localize sound sources in three-dimensionalspace by means of the human binaural sound localization capability.

The input to the hearing consists of two signals, namely the soundpressures at each of the eardrums, in the following termed the binauralsound signals. Thus, if sound pressures at the eardrums that would havebeen generated by a given spatial sound field are accurately reproducedat the eardrums, the human auditory system will not be able todistinguish the reproduced sound from the actual sound generated by thespatial sound field itself.

It is not fully known how the human auditory system extracts informationabout distance and direction to a sound source, but it is known that thehuman auditory system uses a number of cues in this determination. Amongthe cues are spectral cues, reverberation cues, interaural timedifferences (ITD), interaural phase differences (IPD) and interaurallevel differences (ILD).

The transmission of a sound wave from a sound source positioned at agiven direction and distance in relation to the left and right ears ofthe listener is described in terms of two transfer functions, one forthe left ear and one for the right ear, that include any lineardistortion, such as coloration, interaural time differences andinteraural spectral differences. Such a set of two transfer functions,one for the left ear and one for the right ear, is called a Head-RelatedTransfer Function (HRTF). Each transfer function of the HRTF is definedas the ratio between a sound pressure p generated by a plane wave at aspecific point in or close to the appertaining ear canal (p_(L) in theleft ear canal and p_(R) in the right ear canal) in relation to areference. The reference traditionally chosen is the sound pressurep_(l) that would have been generated by a plane wave at a position rightin the middle of the head with the listener absent.

The HRTF contains all information relating to the sound transmission tothe ears of the listener, including diffraction around the head,reflections from shoulders, reflections in the ear canal, etc., andtherefore, the HRTF varies from individual to individual.

In the following, one of the transfer functions of the HRTF will also betermed the HRTF for convenience.

The hearing aid related transfer function is defined similar to a HRTF,namely as the ratio between a sound pressure p generated by the hearingaid at a specific point in the appertaining ear canal in response to aplane wave and a reference. The reference traditionally chosen is thesound pressure p_(l) that would have been generated by a plane wave at aposition right in the middle of the head with the listener absent.

The HRTF changes with direction and distance of the sound source inrelation to the ears of the listener. It is possible to measure the HRTFfor any direction and distance and simulate the HRTF, e.g.electronically, e.g. by filters. If such filters are inserted in thesignal path between a playback unit, such as a tape recorder, andheadphones used by a listener, the listener will achieve the perceptionthat the sounds generated by the headphones originate from a soundsource positioned at the distance and in the direction as defined by thetransfer functions of the filters simulating the HRTF in question,because of the true reproduction of the sound pressures in the ears.

Binaural processing by the brain, when interpreting the spatiallyencoded information, results in several positive effects, namely bettersignal-to-noise ratio (SNR); direction of arrival (DOA) estimation;depth/distance perception and synergy between the visual and auditorysystems.

The complex shape of the ear is a major contributor to the individualspatial-spectral cues (ITD, ILD and spectral cues) of a listener.Devices which pick up sound behind the ear will, hence, be at adisadvantage in reproducing the HRTF since much of the spectral detailwill be lost or heavily distorted.

This is exemplified in FIGS. 1 and 2 where the angular frequencyspectrum of an open ear, i.e. non-occluded, measurement is shown in FIG.1 for comparison with FIG. 2 showing the corresponding measurement onthe front microphone on a behind the ear device (BTE) using the sameear. The open ear spectrum shown in FIG. 1 is rich in detail whereas theBTE result shown in FIG. 2 is much more blurred and much of the spectraldetail is lost.

SUMMARY

It is therefore desirable to position a microphone of the hearing aid ata position with relation to a user wearing the hearing aid, in whichspatial cues of sounds arriving at the user is preserved. It is forexample advantageous to position a microphone in the outer ear of theuser in front of the pinna, for example at the entrance to the earcanal; or, inside the ear canal, in order to preserve spatial cues ofsounds arriving at the ear to a much larger extent than what is possiblewith a microphone positioned behind the ear. A microphone positioned infront of the pinna below the triangular fossa has also provenadvantageous with relation to preservation of spatial cues.

Positioning of a microphone at the entrance to the ear canal or insidethe ear canal leads to the problem that the microphone is moved close tothe sound emitting device of the hearing aid, whereby the risk offeedback generation is increased, which in turn limits the maximumstable gain which can be prescribed with the hearing aid.

The standard way of solving this problem is to completely seal off theear canal using a custom mould. This, however, introduces the occlusioneffect as well as comfort issues with respect to moisture and heat.

For comparison, the maximum stable gain of a BTE hearing aid with frontand rear microphones positioned behind the ear, and an In-The-Ear (ITE)hearing aid with an open fitted microphone positioned in the ear canalis shown in FIG. 3. It can be seen that the ITE hearing aid has muchlower maximum stable gain (MSG) than the front and rear BTE microphonesfor nearly all frequencies.

In the new hearing aid, output signals of an arbitrary configuration ofmicrophones undergo signal processing in such a way that spatial cuesare preserved and conveyed to the user of the hearing aid. The outputsignals are filtered with filters that are configured to preservespatial cues.

The new hearing aid may provide improved localization to the user byproviding, in addition to conventionally positioned microphones as in aBTE hearing aid, at least one ITE microphone intended to be positionedin the outer ear of the user in front of the pinna, e.g. at the entranceto the ear canal or immediately below the triangular fossa; or, insidethe ear canal, when in use, in order to record sound arriving at the earof the user and containing the desired spatial information relating tolocalization of sound sources in the sound environment.

The processor of the new hearing aid combines an audio signal of the atleast one ITE microphone residing in the outer ear of the user with themicrophone signal(s) of the conventionally positioned microphone(s) ofthe hearing aid in such a way that spatial cues are preserved. An audiosignal of the at least one ITE microphone may be formed as a weightedsum of the output signals of each microphone of the at least one ITEmicrophone. Other forms of signal processing may be included in theformation of the audio signal of the at least one ITE microphone.

Thus, a new hearing aid is provided, comprising a BTE hearing aidhousing configured to be worn behind the pinna of a user, at least oneBTE sound input transducer, such as an omni-directional microphone, adirectional microphone, a transducer for an implantable hearing aid, atelecoil, a receiver of a digital audio datastream, etc., accommodatedin the BTE hearing aid housing, each of which is configured forconversion of acoustic sound into a respective audio signal,

an ITE microphone housing configured to be positioned in the outer earof the user for fastening and retaining in its intended position

at least one ITE microphone accommodated in the ITE microphone housing,each of which is configured for conversion of acoustic sound into arespective audio signal, at least one cue filter, each of which havingan input that is provided with an output signal from a respective one ofthe at least one BTE sound input transducer and at least one ITEmicrophone,a processor configured to generate a hearing loss compensated outputsignal based on a combination of the filtered audio signals output bythe at least one cue filter, an output transducer for conversion of thehearing loss compensated output signal to an auditory output signal thatcan be received by the human auditory system, and whereinthe processor is further configured for processing the output signals ofthe at least one ITE microphone and the at least one BTE sound inputtransducer in such a way that the hearing loss compensated output signalsubstantially preserves spatial cues, such as the spatial cues recordedby the at least one ITE microphone, or recorded by a combination of theat least one ITE microphone and the at least one BTE sound inputtransducer.

The hearing aid may further have

a sound signal transmission member for transmission of a signalrepresenting sound from a sound output in the BTE hearing aid housing ata first end of the sound signal transmission member to the ear canal ofthe user at a second end of the sound signal transmission member,an earpiece configured to be inserted in the ear canal of the user forfastening and retaining the sound signal transmission member in itsintended position in the ear canal of the user.

The new hearing aid may be a multi-channel hearing aid in which signalsto be processed are divided into a plurality of frequency channels, andwherein signals are processed individually in each of the frequencychannels. Possible adaptive feedback cancellation circuitry may also bedivided into the plurality of frequency channels; or, the adaptivefeedback cancellation circuitry may still operate in the entirefrequency range; or, may be divided into other frequency channels,typically fewer frequency channels, than the other circuitry is dividedinto.

The processor may be configured for processing the output signals of theat least one ITE microphone and the at least one BTE sound inputtransducer in such a way that the hearing loss compensated output signalsubstantially preserves spatial cues in a selected frequency band.

The selected frequency band may comprise one or more of the frequencychannels, or all of the frequency channels. The selected frequency bandmay be fragmented, i.e. the selected frequency band need not compriseconsecutive frequency channels.

The plurality of frequency channels may include warped frequencychannels, for example all of the frequency channels may be warpedfrequency channels.

Outside the selected frequency band, the at least one ITE microphone maybe connected conventionally as an input source to the processor of thehearing aid and may cooperate with the processor of the hearing aid in awell-known way.

In this way, the at least one ITE microphone supplies the input to thehearing aid at frequencies where the hearing aid is capable of supplyingthe desired gain with this configuration. In the selected frequencyband, wherein the hearing aid cannot supply the desired gain with thisconfiguration, the microphones of BTE hearing aid housing are includedin the signal processing as disclosed above. In this way, the gain canbe increased while simultaneously maintain the spatial information aboutthe sound environment provided by the at least one ITE microphone.

The hearing aid may for example comprise a first filter connectedbetween the processor input and the at least one ITE microphone, and asecond complementary filter connected between the processor input and acombined output of the at least one BTE sound input transducer, thefilters passing and blocking frequencies in complementary frequencybands so that one of the at least one ITE microphone and the combinedoutput of at least one BTE sound input transducer constitutes the mainpart of the input signal supplied to the processor input in onefrequency band, and the other one of the at least one ITE microphone andthe combined output of at least one BTE sound input transducerconstitutes the main part of the input signal supplied to the processorinput in the complementary frequency band.

In this way, the at least one ITE microphone may be used as the soleinput source to the processor in a frequency band wherein the requiredgain for hearing loss compensation can be applied to the output signalof the at least one ITE microphone. Outside this frequency band, thecombined output signal of the at least one BTE sound input transducer isapplied to the processor for provision of the required gain.

Throughout the present disclosure, the “output signals of the at leastone ITE microphone” may be used to identify any analogue or digitalsignal forming part of the signal path from the output of the at leastone ITE microphone to an input of the processor, including pre-processedoutput signals of the at least one ITE microphone.

Likewise, the “output signals of the at least one BTE sound inputtransducer” may be used to identify any analogue or digital signalforming part of the signal path from the at least one BTE sound inputtransducer to an input of the processor, including pre-processed outputsignals of the at least one BTE sound input transducer.

Preferably, the at least one ITE microphone is positioned so that theoutput signal of the at least one ITE microphone generated in responseto the incoming sound has a transfer function that constitutes a goodapproximation to the HRTFs of the user. For example, the at least oneITE microphone may be constituted by a single microphone positioned atthe entrance to the ear canal. The processor conveys the directionalinformation contained in the output signal of the at least one ITEmicrophone to the resulting hearing loss compensated output signal ofthe processor so that the hearing loss compensated output signal of theprocessor also attains a transfer function that constitutes a goodapproximation to the HRTFs of the user whereby improved localization isprovided to the user.

BTE (behind-the-ear) hearings aids are well-known in the art. A BTEhearing aid has a BTE housing that is shaped to be worn behind the pinnaof the user. The BTE housing accommodates components for hearing losscompensation. A sound signal transmission member, i.e. a sound tube oran electrical conductor, transmits a signal representing the hearingloss compensated sound from the BTE housing into the ear canal of theuser.

In order to position the sound signal transmission member securely andcomfortably at the entrance to the ear canal of the user, an earpiece,shell, or earmould may be provided for insertion into the ear canal ofthe user constituting an open solution. In an open solution, theearpiece, shell, or earmould does not obstruct the ear canal when it ispositioned in its intended operational position in the ear canal.Rather, there will be a passageway through the earpiece, shell, orearmould or, between a part of the ear canal wall and a part of theearpiece, shell, or earmould, so that sound waves may escape from behindthe earpiece, shell, or earmould between the ear drum and the earpiece,shell, or earmould through the passageway to the surroundings of theuser. In this way, the occlusion effect is substantially eliminated.

Typically, the earpiece, shell, or earmould is individually custommanufactured or manufactured in a number of standard sizes to fit theuser's ear to sufficiently secure the sound signal transmission memberin its intended position in the ear canal and prevent the earpiece fromfalling out of the ear, e.g., when the user moves the jaw.

The output transducer may be a receiver positioned in the BTE hearingaid housing. In this event, the sound signal transmission membercomprises a sound tube for propagation of acoustic sound signals fromthe receiver positioned in the BTE hearing aid housing and through thesound tube to an earpiece positioned and retained in the ear canal ofthe user and having an output port for transmission of the acousticsound signal to the eardrum in the ear canal.

The output transducer may be a receiver positioned in the earpiece. Inthis event, the sound signal transmission member comprises electricalconductors for propagation of audio signals from the output of aprocessor in the BTE hearing aid housing through the conductors to areceiver positioned in the earpiece for emission of sound through anoutput port of the earpiece.

The ITE microphone housing accommodating at least one ITE microphone maybe combined with, or be constituted by, the earpiece so that the atleast one microphone is positioned proximate the entrance to the earcanal when the earpiece is fastened in its intended position in the earcanal.

The ITE microphone housing may be connected to the earpiece with an arm,possibly a flexible arm that is intended to be positioned inside thepinna, e.g. around the circumference of the conchae abutting theantihelix and at least partly covered by the antihelix for retaining itsposition inside the outer ear of the user. The arm may be pre-formedduring manufacture, preferably into an arched shape with a curvatureslightly larger than the curvature of the antihelix, for easy fitting ofthe arm into its intended position in the pinna. In one example, the armhas a length and a shape that facilitate positioning of the at least oneITE microphone in an operating position immediately below the triangularfossa.

The processor may be accommodated in the BTE hearing aid housing, or inthe ear piece, or part of the processor may be accommodated in the BTEhearing aid housing and part of the processor may be accommodated in theear piece. There is a one-way or two-way communication link betweencircuitry of the BTE hearing aid housing and circuitry of the earpiece.The link may be wired or wireless.

Likewise, there is a one-way or two-way communication link betweencircuitry of the BTE hearing aid housing and the at least one ITEmicrophone. The link may be wired or wireless.

The processor operates to perform hearing loss compensation whilemaintaining spatial information of the sound environment for optimumspatial performance of the hearing aid and while at the same timeproviding as large maximum stable gain as possible.

In the new hearing aid, output signals of an arbitrary configuration ofmicrophones undergo signal processing in such a way that spatial cuesare preserved and conveyed to the user of the hearing aid. The outputsignals are filtered with filters that are configured to preservespatial cues.

For example a method may be performed in the new hearing aid, comprisingthe steps of:

for a set of directions l with relation to the BTE hearing aid,determine

-   -   the Head-Related Transfer functions HRTF_(l)(ƒ),    -   the hearing aid related transfer function H_(l,i) ^(ITEC)(ƒ) of        the i^(th) microphone of the at least one ITE microphone for        direction l,    -   the hearing aid related transfer functions H_(l,j) ^(BTEC)(ƒ) of        the j^(th) microphone of the at least one BTE microphone,        determine the transfer function H_(FB,i) ^(IEC)(ƒ) of the        feedback path associated with the i^(th) microphone of the at        least one ITE microphone,        determine the transfer function H_(FB,j) ^(BTEC)(ƒ) of the        feedback path associated with the j^(th) microphone of the at        least one BTE sound input transducer, and        determine transfer functions G_(i) ^(IEC)(ƒ) of the i^(th) cue        filter of the at least one cue filter filtering audio signals of        the at least one ITE microphone,        determine transfer functions G_(j) ^(BTEC)(ƒ) of the j^(th) cue        filter of at least one cue filter filtering audio signals of the        at least one BTE microphone by solving the following        minimization problem:

$\begin{matrix}{\min\limits_{{G_{i}^{IEC}{(f)}},{G_{i}^{BTEC}{(f)}}}{\sum\limits_{i = 0}^{L - 1}{{{{HRTF}_{l}(f)} - {\quad{{\underset{i}{\quad\sum}{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}} - {\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}}}^{p}}}}} & \;\end{matrix}$wherein p is an integer, e.g. p=2.

Feedback may be taken into account by performing the solution of theminimization problem above subject to the condition that the gain of thefeedback loops must be less than one, i.e. subject to the conditionthat:

$\frac{1}{{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} + {\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}}} \geq {{{MSG}(f)}.}$

Feedback stability may also be ensured by incorporation of the conditioninto the minimization problem:

$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{j}^{BTEC}{(f)}}}\left( {\sum\limits_{l = 0}^{L - 1}\left. {{{HRTF}_{l}(f)} - {\underset{i}{\quad{\quad\sum}}{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}} - {\quad{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}}^{p} + {\alpha{{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} + {\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}}}^{p}}} \right)} \right.$wherein α is a weighting factor balancing spatial cue accuracy andfeedback performance.

Various weights may be incorporated into the minimization problems aboveso that the solution is optimized as specified by the values of theweights. For example, frequency weights W(ƒ) may optimize the solutionin certain one or more frequency ranges, and angular weights W(l) mayoptimize the solution for certain directions of arrival of sound. L (l)is the angular direction towards a sound source with respect to thelooking direction of a user wearing the hearing aid.

Thus, the minimization problem may be modified into:

$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{i}^{BTEC}{(f)}}}{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\left( {{{HRTF}_{l}(f)} - {\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} - {\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}} \right)}}^{p}}}$  subject  to$\mspace{20mu}{\frac{1}{{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} + {\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}}} \geq {{MSG}(f)}}$  or$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{j}^{BTEC}{(f)}}}\left( {{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\left( {{{HRTF}_{l}(f)} - {\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} - {\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}} \right)}}^{p}}} + {\alpha{{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} + {\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}}}^{p}}} \right)$

Further, in one or more selected frequency ranges, only magnitude of thetransfer functions may be taken into account during minimization whilephase is disregarded, i.e. in the one or more selected frequency range,the transfer function is substituted by its absolute value.

The target transfer function need not be defined by the HRTF for thevarious directions l. Any transfer function that includes spatial cuesmay be used as the target transfer function.

For example, one of the ITE microphones of the at least one ITEmicrophone may be positioned at a position with relation to the userwherein the transfer function of the ITE microphone approximates theHRTFs of the user so that HRTF_(l)(ƒ) in the minimization problemsspecified above may be substituted by the transfer function H_(l,ref)^(ITEC)(ƒ) of the ITE microphone in question:

$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{i}^{BTEC}{(f)}}}{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{H_{l,{ref}}^{ITEC}(f)} -} \\{{\sum\limits_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}}$ subject  to$\frac{1}{{{\sum_{i \neq {ref}}{{G_{i}^{{IEC}\;}(f)}{H_{{FB},i}^{IEC}(f)}}} + {\sum_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}}} \geq {{MSG}(f)}$or $\min\limits_{{G_{i}^{IEC}{(f)}},{G_{j}^{BTEC}{(f)}}}\begin{pmatrix}{{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{H_{l,{ref}}^{ITEC}(f)} -} \\{{\sum\limits_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}} +} \\{\alpha{\begin{matrix}{{\sum\limits_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} +} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}\end{matrix}}^{p}}\end{pmatrix}$

The output signal of each of the at least one ITE microphone may bepre-processed.

The output signal of each of the at least one BTE sound input transducermay be pre-processed.

Pre-processing may include, without excluding any form of processing;adaptive and/or static feedback suppression, adaptive or fixedbeamforming and pre-filtering.

The at least one ITE microphone may operate as monitor microphone(s) forgeneration of an electronic sound signal with the desired spatialinformation of the current sound environment.

Each output signal of the at least one BTE sound input transducer and ofthe at least one ITE microphone is filtered with a respective cuefilter, the transfer function of which are configured to provide acombined output signal of the cue filters with a transfer function thatapproximates the HRTFs of the user as closely as possible.

Subsequent to the cue filtering, the combined output signal of the cuefilters is passed on for further hearing loss compensation processing,e.g. with a compressor. In this way, signals from the at least one BTEsound input transducer and the at least one ITE microphone areappropriately processed before hearing loss compensation whereby risk offeedback from the output transducer to the at least one ITE microphoneand the at least one BTE sound input transducer is minimized and a largemaximum stable gain can be provided.

The determinations, for a set of directions l with relation to the newhearing aid, of

-   -   the Head-Related Transfer functions HRTF_(l)(ƒ),    -   the hearing aid related transfer function of the respective at        least one ITE microphone H_(l,i) ^(ITEC)(ƒ), and    -   the hearing aid related transfer functions of the respective at        least one BTE microphone H_(l,j) ^(BTEC)(ƒ)        may be performed with the hearing aid mounted on an artificial        head.

Individual determinations, for a set of directions l with relation tothe new hearing aid, of

-   -   the Head-Related Transfer functions HRTF_(l)(ƒ),    -   the hearing aid related transfer function of the respective at        least one ITE microphone H_(l,i) ^(ITEC)(ƒ), and    -   the hearing aid related transfer functions of the respective at        least one BTE microphone H_(l,i) ^(BTEC)(ƒ)        may be performed for a number of users representing a selected        group of users, and the transfer functions of the at least one        cue filter G_(j) ^(BTEC)(ƒ) of the respective at least one BTE        sound transducer may be determined based on averaged values of    -   the Head-Related Transfer functions HRTF_(l)(ƒ),    -   the hearing aid related transfer function of the respective at        least one ITE microphone H_(l,i) ^(ITEC)(ƒ), and    -   the hearing aid related transfer functions of the respective at        least one BTE microphone H_(l,i) ^(BTEC)(ƒ)        of the number of users representing the selected group of users.

Thus, the at least one cue filter G_(i) ^(IEC)(ƒ) of the respective atleast one ITE microphone and the at least one cue filter G_(j)^(BTEC)(ƒ) of the respective at least one BTE sound transducer may bedetermined by the following steps:

With the hearing aid worn by the individual user:

-   1) Measure the Head-Related Transfer functions HRTF_(l)(ƒ), the    hearing aid related transfer functions H_(l,i) ^(ITEC)(ƒ) and the    hearing aid related transfer functions H_(l,i) ^(BTEC)(ƒ),-   2) Measure the transfer functions H_(FB,i) ^(IEC)(ƒ) of the feedback    path associated with the i^(th) microphone of the at least one ITE    microphone and the transfer functions H_(FB,j) ^(BTEC)(ƒ) of the    feedback paths associated with the j^(th) microphone of the at least    one BTE sound input transducer.-   3) Determine the at least one cue filter G_(i) ^(IEC)(ƒ) of the    respective at least one ITE microphone and the at least one cue    filter G_(j) ^(BTEC)(ƒ) of the respective at least one BTE sound    transducer solving a selected one of the minimization problems    mentioned above.

Some of the measurements above need not be performed with the individualuser; rather measurements may be performed that constitute goodapproximations to individual measurements for a number of humans withcertain characteristics in common, e.g. humans within a certain agegroup, population, etc.:

For a number of user's with certain characteristics in common:

-   1) Measure the Head-Related Transfer functions HRTF_(l)(ƒ), the    hearing aid related transfer functions H_(l,i) ^(ITEC)(ƒ), and the    hearing aid related transfer functions H_(l,i) ^(BTEC)(ƒ) with the    hearing aid mounted on an artificial head, e.g. for a number of    differently sized ears; or, with the hearing aid worn by a number of    humans,-   2) Determine average Head-Related Transfer functions HRTF_(l)(ƒ),    hearing aid related transfer functions H_(l,i) ^(ITEC)(ƒ) and    hearing aid related transfer functions H_(l,i) ^(BTEC)(ƒ) for the    population in question, e.g. one for big ears, one for small ears,    etc, and    For the individual user:-   3) With the hearing aid worn by the individual user: Measure the    transfer functions H_(FB,i) ^(IEC)(ƒ) of the feedback path    associated with the microphone of the at least one ITE microphone    and the transfer functions H_(FB,j) ^(BTEC)(ƒ) of the feedback paths    associated with the j^(th) microphone of the at least one BTE sound    input transducer.-   4) Determine the at least one cue filter G_(i) ^(IEC)(ƒ) of the    respective at least one ITE microphone and the at least one cue    filter G_(j) ^(BTEC)(ƒ) of the respective at least one BTE sound    transducer solving a selected one of the minimization problems    mentioned above.

The audio signals may be divided into a plurality of frequency channels,and be individually processed in individual frequency channels, and thetransfer functions of

-   -   the at least one cue filter G_(i) ^(IEC)(ƒ) of the respective at        least one ITE microphone,    -   the at least one cue filter G_(j) ^(BTEC)(ƒ) of the respective        at least one BTE sound transducer        may be individually determined in selected frequency channels.

The at least one BTE microphone may be disconnected from the processorin one or more selected frequency channels so that hearing losscompensation is performed solely on the output of the at least one ITEmicrophone in the one or more selected frequency channels.

As used herein, the terms “processor”, “signal processor”, “controller”,“system”, etc. (each of which may be considered as an example of a“processing unit”), are intended to refer to CPU-related entities,either hardware, a combination of hardware and software, software, orsoftware in execution.

For example, a “processor”, “signal processor”, “controller”, “system”,etc., may be, but is not limited to being, a process running on aprocessor, a processor, an object, an executable file, a thread ofexecution, and/or a program.

By way of illustration, the terms “processor”, “signal processor”,“controller”, “system”, etc., designate both an application running on aprocessor and a hardware processor. One or more “processors”, “signalprocessors”, “controllers”, “systems” and the like, or any combinationhereof, may reside within a process and/or thread of execution, and oneor more “processors”, “signal processors”, “controllers”, “systems”,etc., or any combination hereof, may be localized on one hardwareprocessor, possibly in combination with other hardware circuitry, and/ordistributed between two or more hardware processors, possibly incombination with other hardware circuitry.

A method of determining parameters of a BTE hearing aid having at leastone ITE microphone and at least one BTE microphone, the method includes:determining Head-Related Transfer functions HRTF_(l)(ƒ); determining ahearing aid related transfer function H_(l,i) ^(IETC)(ƒ) of a i^(th)microphone of the at least one ITE microphone for direction l;determining a hearing aid related transfer functions H_(l,j) ^(BTEC)(ƒ)of a j^(th) microphone of the at least one BTE microphone; determiningtransfer functions G_(i) ^(IEC)(ƒ) of a i^(th) cue filter of at leastone cue filter filtering audio sound signals of the at least one ITEmicrophone; and determining transfer functions G_(j) ^(BTEC)(ƒ) of aj^(th) cue filter of the at least one cue filter filtering audio soundsignals of the at least one BTE microphone; wherein the transferfunctions G_(i) ^(IEC)(ƒ) and the transfer functions G_(j) ^(BTEC)(ƒ)are determined using a processing unit based on an equation:

$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{i}^{BTEC}{(f)}}}{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{{HRTF}_{l}(f)} -} \\{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}}$wherein W(l) is an angular weighting factor, W(ƒ) is a frequencydependent weighting factor, and p is a positive integer.

Optionally, the method may further include determining a transferfunction H_(FB,i) ^(IEC)(ƒ) of a feedback path associated with thei^(th) microphone of the at least one ITE microphone; and determining atransfer function H_(FB,j) ^(BTEC)(ƒ) of a feedback path associated withthe j^(th) microphone of the at least one BTE microphone.

Optionally, the method may further include determining filtercoefficients of the at least one cue filter associated with the at leastone ITE microphone, and filter coefficients of the at least one cuefilter associated with the at least one BTE microphone by solving:

$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{i}^{BTEC}{(f)}}}{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\left( \begin{matrix}{{{HRTF}_{l}(f)} -} \\{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{matrix}\; \right)}}^{p}}}$ subject  to$\frac{1}{{{\sum_{i}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} + {\sum_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}}} \geq {{{MSG}(f)}.}$wherein MSG(f) is a maximum stable gain.

Optionally, the method may further include determining filtercoefficients of the at least one cue filter associated with the at leastone ITE microphone, and filter coefficients of the at least one cuefilter associated with the at least one BTE microphone by solving:

$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{j}^{BTEC}{(f)}}}\begin{pmatrix}{{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{{HRTF}_{l}(f)} -} \\{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}} +} \\{\alpha{\begin{matrix}{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} +} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}\end{matrix}}^{p}}\end{pmatrix}$wherein α is a weighting factor balancing spatial cue accuracy andfeedback performance.

Optionally, the Head-Related Transfer functions HRTF_(l)(ƒ) isdetermined using a hearing aid related transfer function H_(l,ref)^(ITEC)(ƒ), and wherein filter coefficients of the at least one cuefilter filtering audio sound signals of the at least one ITE microphone,and filter coefficients of the at least one cue filter filtering audiosound signals of the at least one BTE microphone are determined bysolving equation:

$\min\limits_{{G_{i\;}^{IEC}{(f)}},{G_{i}^{BTEC}{(f)}}}{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{H_{l,{ref}}^{ITEC}(f)} -} \\{{\sum\limits_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}}$ subject  to$\frac{1}{{{\sum_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} + {\sum_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}}} \geq {{MSG}(f)}$wherein MSG(f) is a maximum stable gain.

Optionally, the Head-Related Transfer functions HRTF_(l)(ƒ) isdetermined using a hearing aid related transfer function H_(l,ref)^(ITEC)(ƒ), and wherein filter coefficients of the at least one cuefilter filtering audio sound signals of the at least one ITE microphone,and filter coefficients of the at least one cue filter filtering audiosound signals of the at least one BTE microphone are determined bysolving equation:

$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{j}^{BTEC}{(f)}}}\begin{pmatrix}{{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{H_{l,{ref}}^{ITEC}(f)} -} \\{{\sum\limits_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}} +} \\{\alpha{\begin{matrix}{{\sum\limits_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} +} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}\end{matrix}}^{p}}\end{pmatrix}$wherein α is a weighting factor balancing spatial cue accuracy andfeedback performance.

Optionally, the acts of determining the Head-Related Transfer functionsHRTF_(l)(ƒ), the hearing aid related transfer function H_(l,i)^(ITEC)(ƒ), and the hearing aid related transfer functions H_(l,i)^(BTEC)(ƒ) are performed with the hearing aid mounted on an artificialhead.

Optionally, the acts of determining the Head-Related Transfer functionsHRTF_(l)(ƒ), the hearing aid related transfer function H_(l,i)^(ITEC)(ƒ), and the hearing aid related transfer functions H_(l,i)^(BTEC)(ƒ) are performed for a number of users; and wherein filtercoefficients of the at least one cue filter filtering audio soundsignals of the at least one BTE microphone are determined based on anaverage value of the Head-Related Transfer functions HRTF_(l)(ƒ), anaverage value of the hearing aid related transfer function H_(l,i)^(ITEC)(ƒ), and an average value of the hearing aid related transferfunctions H_(l,i) ^(BTEC)(ƒ), of the number of users.

Optionally, the hearing aid has a plurality of frequency channels; andwherein filter coefficients of the at least one cue filter filteringaudio sound signals of the at least one ITE microphone, and filtercoefficients of the at least one cue filter filtering audio soundsignals of the at least one BTE microphone are determined in one or moreof the frequency channels.

Optionally, the method may further include disconnecting the at leastone BTE microphone in one or more of the frequency channels so thathearing loss compensation is performed solely on an output of the atleast one ITE microphone.

Optionally, the method may further include generating a hearing losscompensated output signal based on a combination of filtered audio soundsignals output by the at least one cue filter filtering audio soundsignals of the at least one ITE microphone, or by the at least one cuefilter filtering audio sound signals of the at least one BTE microphone,or by both.

Optionally, W(l)=1.

Optionally, W(ƒ)=1.

Optionally, p=2.

An apparatus for determining parameters of a BTE hearing aid having atleast one ITE microphone and at least one BTE microphone, includes aprocessing unit configured for: determining Head-Related Transferfunctions HRTF_(l)(ƒ); determining a hearing aid related transferfunction H_(l,i) ^(ITEC)(ƒ) of a i^(th) microphone of the at least oneITE microphone for direction l; determining a hearing aid relatedtransfer functions H_(l,j) ^(BTEC)(ƒ) of a j^(th) microphone of the atleast one BTE microphone; determining transfer functions G_(i)^(ITEC)(ƒ) of a i^(th) cue filter of at least one cue filter filteringaudio sound signals of the at least one ITE microphone; and determiningtransfer functions G_(j) ^(BTEC)(ƒ) of a j^(th) cue filter of the atleast one cue filter filtering audio sound signals of the at least oneBTE microphone; wherein the processing unit is configured fordetermining the transfer functions G_(i) ^(IEC)(ƒ) and the transferfunctions G_(j) ^(BTEC)(ƒ) based on equation:

$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{i}^{BTEC}{(f)}}}{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{{HRTF}_{l}(f)} -} \\{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}}$wherein W(l) is an angular weighting factor, W(ƒ) is a frequencydependent weighting factor, and p is a positive integer.

Optionally, the processing unit may be further configured for:determining a transfer function H_(FB,i) ^(IEC)(ƒ) of a feedback pathassociated with the i^(th) microphone of the at least one ITEmicrophone; and determining a transfer function H_(FB,j) ^(BTEC)(ƒ) of afeedback path associated with the j^(th) microphone of the at least oneBTE microphone.

Optionally, the processing unit may be further configured for:determining filter coefficients of the at least one cue filterassociated with the at least one ITE microphone, and filter coefficientsof the at least one cue filter associated with the at least one BTEmicrophone by solving:

$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{i}^{BTEC}{(f)}}}{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{{HRTF}_{l}(f)} -} \\{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}}$ subject  to$\frac{1}{{{\sum_{i}{{G_{i\;}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} + {\sum_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}}} \geq {{{MSG}(f)}.}$wherein MSG(f) is a maximum stable gain.

Optionally, the processing unit may be further configured for:determining filter coefficients of the at least one cue filterassociated with the at least one ITE microphone, and filter coefficientsof the at least one cue filter associated with the at least one BTEmicrophone by solving:

$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{j}^{BTEC}{(f)}}}\begin{pmatrix}{{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{{HRTF}_{l}(f)} -} \\{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}} +} \\{\alpha{\begin{matrix}{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} +} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}\end{matrix}}^{p}}\end{pmatrix}$wherein α is a weighting factor balancing spatial cue accuracy andfeedback performance.

Optionally, the Head-Related Transfer functions HRTF_(l)(ƒ) is based ona hearing aid related transfer function H_(l,ref) ^(ITEC)(ƒ), andwherein the processing unit is configured to determine filtercoefficients of the at least one cue filter filtering audio soundsignals of the at least one ITE microphone, and filter coefficients ofthe at least one cue filter filtering audio sound signals of the atleast one BTE microphone by solving equation:

$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{i}^{BTEC}{(f)}}}{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{H_{l,{ref}}^{ITEC}(f)} -} \\{{\sum\limits_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}}$ subject  to$\frac{1}{{{\sum_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} + {\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}}} \geq {{MSG}(f)}$wherein MSG(f) is a maximum stable gain.

Optionally, the Head-Related Transfer functions HRTF_(l)(ƒ) is based ona hearing aid related transfer function H_(l,ref) ^(ITEC)(ƒ), andwherein the processing unit is configured to determine filtercoefficients of the at least one cue filter filtering audio soundsignals of the at least one ITE microphone, and filter coefficients ofthe at least one cue filter filtering audio sound signals of the atleast one BTE microphone by solving equation:

$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{j}^{BTEC}{(f)}}}\begin{pmatrix}{{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{H_{l,{ref}}^{ITEC}(f)} -} \\{{\sum\limits_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}} +} \\{\alpha{\begin{matrix}{{\sum\limits_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} +} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}\end{matrix}}^{p}}\end{pmatrix}$wherein α is a weighting factor balancing spatial cue accuracy andfeedback performance.

Optionally, the processing unit may be configured for determining theHead-Related Transfer functions HRTF_(l)(ƒ), the hearing aid relatedtransfer function H_(l,i) ^(ITEC)(ƒ) and the hearing aid relatedtransfer functions H_(l,i) ^(BTEC)(ƒ) with the hearing aid mounted on anartificial head.

Optionally, the processing unit may be configured for determining theHead-Related Transfer functions HRTF_(l)(ƒ), the hearing aid relatedtransfer function H_(l,i) ^(ITEC)(ƒ), and the hearing aid relatedtransfer functions H_(l,i) ^(BTEC)(ƒ) for a number of users; and whereinthe processing unit may be configured to determine filter coefficientsof the at least one cue filter filtering audio sound signals of the atleast one BTE microphone based on an average value of the Head-RelatedTransfer functions HRTF_(l)(ƒ), an average value of the hearing aidrelated transfer function H_(l,i) ^(ITEC)(ƒ), and an average value ofthe hearing aid related transfer functions H_(l,i) ^(BTEC)(ƒ), of thenumber of users.

Optionally, the BTE hearing aid may have a plurality of frequencychannels; and wherein the processing unit may be configured fordetermining filter coefficients of the at least one cue filter filteringaudio sound signals of the at least one ITE microphone, and filtercoefficients of the at least one cue filter filtering audio soundsignals of the at least one BTE microphone, in one or more of thefrequency channels.

Optionally, the processing unit may be further configured fordisconnecting the at least one BTE microphone in one or more of thefrequency channels so that hearing loss compensation is performed solelyon an output of the at least one ITE microphone.

Optionally, the processing unit may be further configured for generatinga hearing loss compensated output signal based on a combination offiltered audio sound signals output by the at least one cue filterfiltering audio sound signals of the at least one ITE microphone, or bythe at least one cue filter filtering audio sound signals of the atleast one BTE microphone, or by both.

Optionally, W(l)=1.

Optionally, W(ƒ)=1.

Optionally, p=2.

Other and further aspects and features will be evident from reading thefollowing detailed description of the embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of embodiments, in whichsimilar elements are referred to by common reference numerals. Thesedrawings are not necessarily drawn to scale. In order to betterappreciate how the above-recited and other advantages and objects areobtained, a more particular description of the embodiments will berendered, which are illustrated in the accompanying drawings. Thesedrawings depict only exemplary embodiments and are not therefore to beconsidered limiting in the scope of the claims.

FIG. 1 shows a plot of the angular frequency spectrum of an open ear,

FIG. 2 shows a plot of the angular frequency spectrum of a BTE frontmicrophone worn at the same ear,

FIG. 3 shows plots of maximum stable gain of a BTE front and rearmicrophones and an open fitted ITE microphone positioned in the earcanal,

FIG. 4 schematically illustrates an exemplary new hearing aid,

FIG. 5 schematically illustrates another exemplary new hearing aid,

FIG. 6 shows in perspective a new hearing aid with an ITE-microphone inthe outer ear of a user,

FIG. 7 shows a schematic block diagram of an exemplary new hearing aidwith cue filters,

FIG. 8 shows a schematic block diagram of the new hearing aid of FIG. 7with added feedback cancellation, and

FIG. 9 shows a schematic block diagram illustrating one method ofdetermining the cue filters.

DETAILED DESCRIPTION

Various embodiments are described hereinafter with reference to thefigures. It should be noted that the figures are not necessarily drawnto scale and that elements of similar structures or functions arerepresented by like reference numerals throughout the figures. It shouldalso be noted that the figures are only intended to facilitate thedescription of the embodiments. They are not intended as an exhaustivedescription of the claimed invention or as a limitation on the scope ofthe claimed invention. In addition, an illustrated embodiment needs nothave all the aspects or advantages shown. An aspect or an advantagedescribed in conjunction with a particular embodiment is not necessarilylimited to that embodiment and can be practiced in any other embodimentseven if not so illustrated, or if not so explicitly described.

FIG. 4 schematically illustrates an example of the new hearing aid 10comprising a BTE hearing aid housing 12 (not shown—outer walls have beenremoved to make internal parts visible) to be worn behind the pinna 100of a user. The BTE housing 12 accommodates at least one BTE sound inputtransducer 14, 16 with a front microphone 14 and a rear microphone 16for conversion of a sound signal into a microphone audio signal,optional pre-filters (not shown) for filtering the respective microphoneaudio signals, A/D converters (not shown) for conversion of therespective microphone audio signals into respective digital microphoneaudio signals that are input to a processor 18 configured to generate ahearing loss compensated output signal based on the input digital audiosignals.

The hearing loss compensated output signal is transmitted throughelectrical wires contained in a sound signal transmission member 20 to areceiver 22 for conversion of the hearing loss compensated output signalto an acoustic output signal for transmission towards the eardrum of auser and contained in an earpiece 24 that is shaped (not shown) to becomfortably positioned in the ear canal of a user for fastening andretaining the sound signal transmission member in its intended positionin the ear canal of the user as is well-known in the art of BTE hearingaids.

The earpiece 24 also holds one ITE microphone 26 that is positioned atthe entrance to the ear canal when the earpiece is positioned in itsintended position in the ear canal of the user. The ITE microphone 26 isconnected to an A/D converter (not shown) and optional to a pre-filter(not shown) in the BTE housing 12, with electrical wires (not visible)contained in the sound transmission member 20.

The BTE hearing aid 10 is powered by battery 28.

Various possible functions of the processor 18 are disclosed above andsome of these in more detail below.

FIG. 5 schematically illustrates another BTE hearing aid 10 similar tothe hearing aid shown in FIG. 1, except for the difference that in FIG.5, the receiver 22 is positioned in the hearing aid housing 12 and notin the earpiece 24, so that acoustic sound output by the receiver 22 istransmitted through the sound tube 20 and towards the eardrum of theuser when the earpiece 24 is positioned in its intended position in theear canal of the user.

The positioning of the ITE microphone 26 proximate the entrance to theear canal of the user when the BTE hearing aids 10 of FIGS. 4 and 5 areused is believed to lead to a good reproduction of the HRTFs of theuser.

FIG. 6 shows a BTE hearing aid 10 in its operating position with the BTEhousing 12 behind the ear, i.e. behind the pinna 100, of the user. Theillustrated BTE hearing aid 10 is similar to the hearing aids shown inFIGS. 4 and 5 except for the fact that the ITE microphone 26 ispositioned in the outer ear of the user outside the ear canal at thefree end of an arm 30. The arm 30 is flexible and the arm 30 is intendedto be positioned inside the pinna 100, e.g. around the circumference ofthe conchae 102 behind the tragus 104 and antitragus 106 and abuttingthe antihelix 108 and at least partly covered by the antihelix forretaining its position inside the outer ear of the user. The arm may bepre-formed during manufacture, preferably into an arched shape with acurvature slightly larger than the curvature of the antihelix 108, foreasy fitting of the arm 30 into its intended position in the pinna. Thearm 30 contains electrical wires (not visible) for interconnection ofthe ITE microphone 26 with other parts of the BTE hearing aid circuitry.

In one example, the arm 30 has a length and a shape that facilitatepositioning of the ITE microphone 26 in an operating position below thetriangular fossa.

FIG. 7 is a block diagram illustrating one example of signal processingin the new hearing aid 10. The BTE hearing aid 10 has an array ofmicrophones 14-1, 14-2, . . . , 14-M, 26-1, 26-2, . . . , 26-N, forexample constituted by a front microphone 14 and a rear microphone 16and an ITE microphone 26 that resides in an earpiece 24 to be positionedin the outer ear of the user as illustrated in FIGS. 4-6. N and M can beany integer, e.g. N=1, and M=2.

The microphone output audio signals are digitized (A/D-converters notshown) and pre-processed, such as pre-filtered, in respectivepre-processors 32-1, 32-2, . . . , 32-N, 34-1, 34-2, . . . , 34-M. Thedigitized and possibly pre-processed microphone output audio signals38-1, 38-2, . . . , 38-N, 40-1, 40-2, . . . , 40-M are filtered in cuefilters 42-1, 42-2, . . . , 42-N, 44-1, 44-2, . . . , 44-M and thefiltered signals 46-1, 46-2, . . . , 46-N, 48-1, 48-2, . . . , 48-M areadded to each other in adder 50 and the combined signal 52 is input to aprocessor 18 for hearing loss compensation. The hearing loss compensatedsignal 54 is output to a receiver 22 that converts the signal to anacoustic signal for transmission towards the ear drum of the user.

The new hearing aid circuitry shown in FIG. 7 may operate in the entirefrequency range of the BTE hearing aid 10.

The hearing aid 10 shown in FIG. 7 may be a multi-channel hearing aid inwhich microphone output audio signals are divided into a plurality offrequency channels, and wherein divided signals are processedindividually in each of the frequency channels.

For a multi-channel hearing aid 10, FIG. 7 may illustrate the circuitryand signal processing in a single frequency channel. The circuitry andsignal processing may be duplicated in a plurality of the frequencychannels, e.g. in all of the frequency channels.

For example, the signal processing illustrated in FIG. 7 may beperformed in a selected frequency band, e.g. selected during fitting ofthe hearing aid 10 to a specific user at a dispenser's office.

The selected frequency band may comprise one or more of the frequencychannels, or all of the frequency channels. The selected frequency bandmay be fragmented, i.e. the selected frequency band need not compriseconsecutive frequency channels.

The plurality of frequency channels may include warped frequencychannels, for example all of the frequency channels may be warpedfrequency channels.

Outside the selected frequency band, one or more of the at least one ITEmicrophone may be connected conventionally as an input source to theprocessor of the hearing aid and may cooperate with the processor of thehearing aid in a well-known way.

In this way, one or more or all of the at least one ITE microphoneprovide the input to the processor 18 at frequencies where the hearingaid is capable of supplying the desired gain based on the input from theone or more of the at least one ITE microphone. In the selectedfrequency band, wherein the hearing aid cannot supply the desired gainwith this configuration, the microphones of BTE hearing aid housing areincluded in the signal processing as disclosed above. In this way, thegain can be increased while simultaneously maintain the spatialinformation about the sound environment as provided by the array ofmicrophones.

The transfer functions of the Cue filters 42-1, 42-2, . . . , 42-N,44-1, 44-2, . . . , 44-M has been determined before use, e.g. at thedispenser's office, by the following steps:

-   1) Measure the Head-Related Transfer functions HRTF_(l)(ƒ), the    hearing aid related transfer functions H_(l,i) ^(ITEC)(ƒ) and the    hearing aid related transfer functions H_(l,i) ^(BTEC)(ƒ) with the    hearing aid mounted on an artificial head, e.g. for a number of    differently sized ears; or, with the hearing aid worn by a number of    humans,-   2) Determine average Head-Related Transfer functions HRTF_(l)(ƒ),    hearing aid related transfer functions H_(l,i) ^(ITEC)(ƒ) and    hearing aid related transfer functions H_(l,i) ^(BTEC)(ƒ) for the    population in question, e.g. one for big ears, one for small ears,    etc,-   3) With the hearing aid worn by the individual user: Measure the    transfer functions H_(FB,i) ^(IEC)(ƒ) of the feedback path    associated with the microphone of the at least one ITE microphone    and the transfer functions H_(FB,j) ^(BTEC)(ƒ) of the feedback paths    associated with the j^(th) microphone of the at least one BTE sound    input transducer.-   4) Determine the transfer function of the at least one cue filter    G_(l) ^(IEC)(ƒ) and the at least one cue filter G_(j) ^(BTEC)(ƒ)    solving a selected one of the following minimization problems:

$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{i}^{BTEC}{(f)}}}{\sum\limits_{l = 0}^{L - 1}{\begin{matrix}\begin{matrix}{{{HRTF}_{l}(f)} -} \\{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -}\end{matrix} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{matrix}}^{p}}$wherein p is an integer, e.g. p=2.

In order to ensure feedback stability, the minimization problem may besolved subject to the condition that:

$\frac{1}{{{\sum_{i}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} + {\sum_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}}} \geq {{{MSG}(f)}.}$

Feedback stability may also be ensured by incorporation of the conditioninto the minimization problem:

$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{j}^{BTEC}{(f)}}}\begin{pmatrix}{{\sum\limits_{l = 0}^{L - 1}{\begin{matrix}\begin{matrix}{{{HRTF}_{l}(f)} -} \\{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -}\end{matrix} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{matrix}}^{p}} +} \\{\alpha{\begin{matrix}{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} +} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}\end{matrix}}}\end{pmatrix}$wherein α is a weighting factor balancing spatial cue accuracy andfeedback performance.

Various weights may be incorporated into the minimization problems aboveso that the solution is optimized as specified by the values of theweights. For example, frequency weights W(ƒ) may optimize the solutionin certain one or more frequency ranges, and angular weights W(l) mayoptimize the solution for certain directions of arrival of sound. Thus,the minimization problem may be modified into:

$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{i}^{BTEC}{(f)}}}{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}\begin{matrix}{{{HRTF}_{l}(f)} -} \\{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -}\end{matrix} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}}$ subject  to$\frac{1}{{{\sum_{i}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} + {\sum_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}}} \geq {{MSG}(f)}$or $\min\limits_{{G_{i}^{IEC}{(f)}},{G_{j}^{BTEC}{(f)}}}\begin{pmatrix}{{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{{HRTF}_{l}(f)} -} \\{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}} +} \\{\alpha{\begin{matrix}{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} +} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}\end{matrix}}^{p}}\end{pmatrix}$

Further, in one or more selected frequency ranges, only magnitude of thetransfer functions may be taken into account during minimization whilephase is disregarded, i.e. in the one or more selected frequency range,the transfer function is substituted by its absolute value.

The target transfer function need not be defined by the HRTF for thevarious directions l. Any transfer function that includes spatial cuesmay be used as the target transfer function.

For example, one of the ITE microphones of the at least one ITEmicrophone may be positioned at a position with relation to the userwherein the transfer function of the ITE microphone approximates theHRTFs of the user so that HRTF_(l)(ƒ) in the minimization problemsspecified above may be substituted by the transfer function H_(l,ref)^(ITEC)(ƒ) of the ITE microphone in question:

$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{i}^{BTEC}{(f)}}}{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{H_{l,{ref}}^{ITEC}(f)} - {\sum\limits_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}}$   subject  to$\mspace{20mu}{\frac{1}{{{\sum_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} + {\sum_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}}} \geq {{MSG}(f)}}$  or$\mspace{20mu}{\min\limits_{{G_{i}^{IEC}{(f)}},{G_{j}^{BTEC}{(f)}}}\begin{pmatrix}{{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}\begin{matrix}{{H_{l,{ref}}^{ITEC}(f)} -} \\{{\sum\limits_{i \neq {ref}}{G_{i}^{IEC}(f){H_{l,i}^{IEC}(f)}}} -}\end{matrix} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}} +} \\{\alpha{\begin{matrix}{{\sum\limits_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} +} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}\end{matrix}}^{p}}\end{pmatrix}}$

FIG. 8 is a block diagram illustrating a new hearing aid 10 similar tothe hearing aid 10 shown in FIG. 7 except for the fact that an adaptivefeedback canceller 70 has been added with an input 72 connected to theoutput of the processor 18 and outputs 74-1, 74-2, . . . , 74-N, 76-1,76-2, . . . , 76-M connected to respective subtractors 78-1, 78-2, . . ., 78-N. 80-1, 80-2, . . . , 80-M for subtraction of the outputs fromeach respective microphone output audio signal to provide feedbackcompensated signals fed to the corresponding pre-processors 32-1, 32-2,. . . , 32-N, 34-1, 34-2, . . . , 34-M and to the feedback canceller 70for control of the adaption of the feedback canceller 70 comprisingadaptive filters as is well-known in the art. The feedback canceller 70provide signals 74-1, 74-2, . . . , 74-N, 76-1, 76-2, . . . , 76-M thatconstitute approximations of corresponding feedback signals travellingfrom the output transducer 22 to the respective microphones 14-1, 14-2,. . . , 14-M, 26-1, 26-2, . . . , 26-N.

The hearing aid 10 shown in FIG. 8 may be a multi-channel hearing aid inwhich microphone output audio signals are divided into a plurality offrequency channels, and wherein divided signals are processedindividually in each of the frequency channels.

For a multi-channel hearing aid 10, FIG. 8 may illustrate the circuitryand signal processing in a single frequency channel. The circuitry andsignal processing may be duplicated in a plurality of the frequencychannels, e.g. in all of the frequency channels. The adaptive feedbackcancelling circuitry may also be divided into the plurality of frequencychannels; or, the adaptive circuitry may still operate in the entirefrequency range; or, may be divided into other frequency channels,typically fewer frequency channels, than the other circuitry is dividedinto.

For example, the signal processing illustrated in FIG. 8 may beperformed in a selected frequency band, e.g. selected during fitting ofthe hearing aid 10 to a specific user at a dispenser's office.

The selected frequency band may comprise one or more of the frequencychannels, or all of the frequency channels. The selected frequency bandmay be fragmented, i.e. the selected frequency band need not compriseconsecutive frequency channels.

The plurality of frequency channels may include warped frequencychannels, for example all of the frequency channels may be warpedfrequency channels.

Outside the selected frequency band, one or more of the at least one ITEmicrophone may be connected conventionally as an input source to theprocessor of the hearing aid and may cooperate with the processor of thehearing aid in a well-known way.

In this way, the one or more of the at least one ITE microphone providethe input to the processor 18 at frequencies where the hearing aid iscapable of supplying the desired gain based on the input from the one ormore of the at least one ITE microphone. In the selected frequency band,wherein the hearing aid cannot supply the desired gain with thisconfiguration, the microphones of BTE hearing aid housing are includedin the signal processing as disclosed above. In this way, the gain canbe increased while simultaneously maintain the spatial information aboutthe sound environment as provided by the array of microphones.

The transfer functions of the Cue filters 42-1, 42-2, . . . , 42-N,44-1, 44-2, . . . , 44-M has been determined before use, e.g. at thedispenser's office, by the same steps as disclosed above in connectionwith FIG. 7.

FIG. 9 is a schematic block diagram illustrating one method ofdetermining the cue filters 42-1, 42-2, . . . , 42-N, 44-1, 44-2, . . ., 44-M of the hearing aids shown in FIGS. 7 and 8, e.g. during fittingof the hearing aid.

The cue filters 42-1, 42-2, . . . , 42-N, 44-1, 44-2, . . . , 44-M areadaptive filters that are allowed to adapt during fitting of the hearingaid. After determination of the cue filters, the filter coefficients arekept constant at the respective determined values.

The microphone ITE_(REF) 25 may be a single microphone located in aposition with relation to an artificial head or a user with goodpreservation of spatial cues of incoming sound; or, the microphoneITE_(REF) 25 may represent an array of microphones connected topre-processor 31 and located in a position with relation to anartificial head or a user in which a combined signal output from thearray of microphones, e.g. in cooperation with pre-processor 31, hasgood preservation of spatial cues of incoming sound.

Due to the positioning of microphone (array) ITE_(REF) 25, the outputsignal of microphone (array) ITE_(REF) 25 has a transfer function thatconstitutes a good approximation to the HRTFs of the user for one ormore directions towards a sound source.

During fitting, various sound sources emit sound from respective variousdirections with relation to the artificial head or user of the hearingaid, and the cue filters 42-1, 42-2, . . . , 42-N, 44-1, 44-2, . . . ,44-M are allowed to adapt to the output signal 51 of the delay 41 and atthe end of adaptation, e.g. when the filter coefficients of the cuefilters 42-1, 42-2, . . . , 42-N, 44-1, 44-2, . . . , 44-M havestabilized, i.e. the changes of the filter coefficients have become lessthan a certain threshold, the filter coefficients are no longer allowedto change. Further, the signal 51 is disconnected from subtractor 54 sothat signal 56 constitutes a combined output signal of the cue filters42-1, 42-2, . . . , 42-N, 44-1, 44-2, . . . , 44-M that hassubstantially the same spatial cues as the output signal 51.

The delay 41 delays the output signal of the pre-processor 31 with adelay that is substantially equal to the delay of the cue filters 42-1,42-2, . . . , 42-N, 44-1, . . . , 44-M.

During determination of the filter coefficients of the cue filters 42-1,42-2, . . . , 42-N, 44-1, . . . , 44-M, e.g. during fitting, adaptationof the filter coefficients of the cue filters 42-1, 42-2, . . . , 42-N,44-1, . . . , 44-M are controlled by adaptive cue controller 48 thatcontrols the adaptation of the filter coefficients to minimize theoutput signal 52 of the subtractor 54 equal to the difference betweensum of output signals 50-1, 50-2, . . . , 50-N, 46-1, 46-2, . . . , 46-Mand the ITE_(REF) microphone audio signal 51.

Thus, while adapting, the adaptive cue control 48 operates to adjust thefilter coefficients of the cue filters 42-1, 42-2, . . . , 42-N, 44-1,44-2, . . . , 44-M solving the following minimization problem:

$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{i}^{BTEC}{(f)}}}{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{H_{l,{ref}}^{ITEC}(f)} - {\sum\limits_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}}$whereinW(ƒ) are frequency weights that may optimize the solution in certain oneor more frequency ranges, andW(l) are angular weights that may optimize the solution for certaindirections of arrival of sound.W(ƒ) may be equal to one for all frequencies and/or W(l) may be equal toone for all directions.

Possible feedback may be taken into account by solving the minimizationproblem above subject to the condition that

$\frac{1}{{{\sum_{i}{{G_{i}^{IEC}(f)}H_{{FB},i}^{IEC}}} + {\sum_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}}} \geq {{MSG}(f)}$or $\min\limits_{{G_{i}^{IEC}{(f)}},{G_{j}^{BTEC}{(f)}}}\begin{pmatrix}{{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{W(f)\begin{pmatrix}\begin{matrix}{{{HRTF}_{l}(f)} -} \\{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -}\end{matrix} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}} +} \\{\alpha{\begin{matrix}{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} +} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}\end{matrix}}^{p}}\end{pmatrix}$

For example, the feedback compensation circuitry 72, 70, 74-1, 74-2, . .. , 74-N, 76-1, 76-2, . . . , 76-M, 78-1, 78-2, . . . , 78-N, 80-1,80-2, . . . , 80-M, 82-1, 82-2, . . . , 82-N, 84-1, 84-2, . . . , 84-M,shown in FIG. 8 may be added to the circuit of FIG. 9 and in additionconnecting the outputs 74-1, 74-2, . . . , 74-N, 76-1, 76-2, . . . ,76-M of the adaptive feedback filter 70 to respective inputs of theadaptive cue control 48, each of the outputs 74-1, 74-2, . . . , 74-N,76-1, 76-2, . . . , 76-M providing an estimate of the hearing aidrelated transfer function of the respective at least one ITE microphoneH_(l,i) ^(ITEC)(l) and the hearing aid related transfer functions of therespective at least one BTE microphone H_(l,j) ^(BTEC)(ƒ) so that theadaptive cue control 48 can check the condition:

$\frac{1}{{{\sum_{i}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} + {\sum_{j}{{G_{j}^{BTEC}(f)}H_{{FB},j}^{BTEC}}}}} \geq {{MSG}(f)}$or solve the minimization problem:

$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{j}^{BTEC}{(f)}}}\begin{pmatrix}{{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}\begin{matrix}{{{HRTF}_{l}(f)} -} \\{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -}\end{matrix} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}} +} \\{\alpha{\begin{matrix}{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} +} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}\end{matrix}}^{p}}\end{pmatrix}$

Although particular embodiments have been shown and described, it willbe understood that it is not intended to limit the claimed inventions tothe preferred embodiments, and it will be obvious to those skilled inthe art that various changes and modifications may be made withoutdeparting from the spirit and scope of the claimed inventions. Thespecification and drawings are, accordingly, to be regarded in anillustrative rather than restrictive sense. The claimed inventions areintended to cover alternatives, modifications, and equivalents.

The invention claimed is:
 1. A method of determining parameters of abehind-the-ear (BTE) hearing aid having at least one in-the-ear (ITE)microphone and at least one BTE microphone, the method comprising:determining transfer functions that include spatial cues; determining ahearing aid related transfer function H_(l,i) ^(IEC)(ƒ) of a i^(th)microphone of the at least one ITE microphone for direction l;determining a hearing aid related transfer functions H_(l,j) ^(BTEC)(ƒ)of a j^(th) microphone of the at least one BTE microphone; determiningtransfer functions G_(i) ^(IEC)(ƒ) of a i^(th) cue filter of at leastone cue filter filtering audio sound signals of the at least one ITEmicrophone; and determining transfer functions G_(j) ^(BTEC)(ƒ) of ai^(th) cue filter of the at least one cue filter filtering audio soundsignals of the at least one BTE microphone; wherein the transferfunctions G_(i) ^(IEC)(ƒ) and the transfer functions G_(j) ^(BTEC)(ƒ)are determined using a processing unit in the BTE hearing aid, theprocessing unit configured to solve a minimization problem based on thetransfer functions that include the spatial cues, the hearing aidrelated transfer function H_(l,i) ^(IEC)(ƒ), and the hearing aid relatedtransfer function H_(l,j) ^(BTEC)(ƒ).
 2. The method according to claim1, further comprising: determining a transfer function H_(FB,i)^(IEC)(ƒ) of a feedback path associated with the i^(th) microphone ofthe at least one ITE microphone; and determining a transfer functionH_(FB,j) ^(BTEC)(ƒ) of a feedback path associated with the j^(th)microphone of the at least one BTE microphone.
 3. The method accordingto claim 2, further comprising: determining filter coefficients of theat least one cue filter associated with the at least one ITE microphone,and filter coefficients of the at least one cue filter associated withthe at least one BTE microphone by solving:$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{i}^{BTEC}{(f)}}}{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{{HRTF}_{l}(f)} -} \\{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}}$ subject  to$\frac{1}{{{\sum_{i}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} + {\sum_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}}} \geq {{{MSG}(f)}.}$wherein MSG(f) is a maximum stable gain, or by solving: $\begin{matrix}{\min\limits_{{G_{i}^{IEC}{(f)}},{G_{j}^{BTEC}{(f)}}}\begin{pmatrix}{{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{{HRTF}_{l}(f)} -} \\{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}} +} \\{\alpha{\begin{matrix}{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} +} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}\end{matrix}}^{p}}\end{pmatrix}} & \;\end{matrix}$ wherein α is a weighting factor balancing spatial cueaccuracy and feedback performance, p is an integer, W(l) is angularweight(s), and W(ƒ) is frequency weight(s).
 4. The method according toclaim 2, wherein the transfer functions that include spatial cuescomprise Head-Related Transfer functions HRTF_(l)(ƒ); and wherein theHead-Related Transfer functions HRTF_(l)(ƒ) are determined using ahearing aid related transfer function H_(l,ref) ^(ITEC)(ƒ), and whereinfilter coefficients of the at least one cue filter filtering audio soundsignals of the at least one ITE microphone, and filter coefficients ofthe at least one cue filter filtering audio sound signals of the atleast one BTE microphone are determined by solving equation:$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{i}^{BTEC}{(f)}}}{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}\begin{matrix}{{H_{l,{ref}}^{ITEC}(f)} -} \\{{\sum\limits_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -}\end{matrix} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}}$ subject  to$\frac{1}{{{\sum_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} + {\sum_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}}} \geq {{MSG}(f)}$wherein MSG(f) is a maximum stable gain, p is an integer, W(l) isangular weight(s), and W(ƒ) is frequency weight(s).
 5. The methodaccording to claim 2, wherein the transfer functions that includespatial cues comprise Head-Related Transfer functions HRTF_(l)(ƒ); andwherein the Head-Related Transfer functions HRTF_(l)(ƒ) are determinedusing a hearing aid related transfer function H_(l,ref) ^(ITEC)(ƒ), andwherein filter coefficients of the at least one cue filter filteringaudio sound signals of the at least one ITE microphone, and filtercoefficients of the at least one cue filter filtering audio soundsignals of the at least one BTE microphone are determined by solvingequation:$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{j}^{BTEC}{(f)}}}\begin{pmatrix}{{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{H_{l,{ref}}^{ITEC}(f)} -} \\{{\sum\limits_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}} +} \\{\alpha{\begin{matrix}{{\sum\limits_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} +} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}\end{matrix}}^{p}}\end{pmatrix}$ wherein α is a weighting factor balancing spatial cueaccuracy and feedback performance, p is an integer, W(l) is angularweight(s), and W(ƒ) is frequency weight(s).
 6. The method according toclaim 1, wherein the transfer functions that include spatial cuescomprise Head-Related Transfer functions HRTF_(l)(ƒ); and wherein theacts of determining the Head-Related Transfer functions HRTF_(l)(ƒ), thehearing aid related transfer function H_(l,i) ^(IEC)(ƒ), and the hearingaid related transfer functions H_(l,i) ^(BTEC)(ƒ) are performed with thehearing aid mounted on an artificial head.
 7. The method according toclaim 1, wherein the transfer functions that include spatial cuescomprise Head-Related Transfer functions HRTF_(l)(ƒ); and wherein theacts of determining the Head-Related Transfer functions HRTF_(l)(ƒ), thehearing aid related transfer function H_(l,i) ^(IEC)(ƒ), and the hearingaid related transfer functions H_(l,i) ^(BTEC)(ƒ) are performed for anumber of users; and wherein filter coefficients of the at least one cuefilter filtering audio sound signals of the at least one BTE microphoneare determined based on an average value of the Head-Related Transferfunctions HRTF_(l)(ƒ), an average value of the hearing aid relatedtransfer function H_(l,i) ^(ITEC)(ƒ), and an average value of thehearing aid related transfer functions H_(l,i) ^(BTEC)(ƒ), of the numberof users.
 8. The method according to claim 1, wherein the hearing aidhas a plurality of frequency channels; and wherein filter coefficientsof the at least one cue filter filtering audio sound signals of the atleast one ITE microphone, and filter coefficients of the at least onecue filter filtering audio sound signals of the at least one BTEmicrophone are determined in one or more of the frequency channels. 9.The method according to claim 8, further comprising disconnecting the atleast one BTE microphone in one or more of the frequency channels sothat hearing loss compensation is performed solely on an output of theat least one ITE microphone.
 10. The method according to claim 1,further comprising generating a hearing loss compensated output signalbased on a combination of filtered audio sound signals output by the atleast one cue filter filtering audio sound signals of the at least oneITE microphone, or by the at least one cue filter filtering audio soundsignals of the at least one BTE microphone, or by both.
 11. The methodaccording to claim 1, wherein the transfer functions that includespatial cues comprise Head-Related Transfer functions HRTF_(l)(ƒ) andthe minimization problem is based on the equation: $\begin{matrix}{\min\limits_{{G_{i}^{IEC}{(f)}},{G_{i}^{BTEC}{(f)}}}{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{{HRTF}_{l}(f)} -} \\{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}}} & \;\end{matrix}$ wherein W(l) is an angular weighting factor, W(ƒ) is afrequency dependent weighting factor, and p is a positive integer. 12.The method according to claim 11, wherein W(l)=1.
 13. The methodaccording to claim 11, wherein W(ƒ)=1.
 14. The method according to claim11, wherein p=2.
 15. An apparatus for determining parameters of abehind-the-ear (BTE) hearing aid having at least one in-the-ear (ITE)microphone and at least one BTE microphone, the apparatus comprising aprocessing unit, wherein the processing unit comprises at least somehardware and is configured for: determining transfer functions thatinclude spatial cues; determining a hearing aid related transferfunction H_(l,i) ^(IEC)(ƒ) of a i^(th) microphone of the at least oneITE microphone for direction l; determining a hearing aid relatedtransfer functions H_(l,j) ^(BTEC)(ƒ) of a j^(th) microphone of the atleast one BTE microphone; determining transfer functions G_(i) ^(IEC)(ƒ)of a i^(th) cue filter of at least one cue filter filtering audio soundsignals of the at least one ITE microphone; and determining transferfunctions G_(j) ^(BTEC)(ƒ) of a j^(th) cue filter of the at least onecue filter filtering audio sound signals of the at least one BTEmicrophone; wherein the processing unit is configured for determiningthe transfer functions G_(i) ^(IEC)(ƒ) and the transfer functions G_(j)^(BTEC)(ƒ) by solving a minimization problem based on the transferfunctions that include the spatial cues, the hearing aid relatedtransfer function H_(l,i) ^(IEC)(ƒ), and the hearing aid relatedtransfer function H_(l,j) ^(BTEC)(ƒ).
 16. The apparatus according toclaim 15, wherein the processing unit is further configured for:determining a transfer function H_(FB,i) ^(IEC)(ƒ) of a feedback pathassociated with the i^(th) microphone of the at least one ITEmicrophone; and determining a transfer function H_(FB,j) ^(BTEC)(ƒ) of afeedback path associated with the j^(th) microphone of the at least oneBTE microphone.
 17. The apparatus according to claim 16, wherein theprocessing unit is further configured for: determining filtercoefficients of the at least one cue filter associated with the at leastone ITE microphone, and filter coefficients of the at least one cuefilter associated with the at least one BTE microphone by solving:$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{i}^{BTEC}{(f)}}}{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{{HRTF}_{l}(f)} -} \\{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}}$ subject  to$\frac{1}{{{\sum_{i}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} + {\sum_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}}} \geq {{MSG}(f)}$wherein MSG(f) is a maximum stable gain, or by solving:$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{j}^{BTEC}{(f)}}}\begin{pmatrix}{{\sum\limits_{l = 0}^{L - 1}{{{W(f)}\begin{pmatrix}{{{HRTF}_{l}(f)} -} \\{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}} +} \\{\alpha{\begin{matrix}{{\sum\limits_{i}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} +} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}\end{matrix}}^{p}}\end{pmatrix}$ wherein α is a weighting factor balancing spatial cueaccuracy and feedback performance, p is an integer, W(l) is angularweight(s), and W(ƒ) is frequency weight(s).
 18. The apparatus accordingto claim 16, wherein the transfer functions that include spatial cuescomprise Head-Related Transfer functions HRTF_(l)(ƒ); and wherein theHead-Related Transfer functions HRTF_(l)(ƒ) are based on a hearing aidrelated transfer function H_(l,ref) ^(ITEC)(ƒ), and wherein theprocessing unit is configured to determine filter coefficients of the atleast one cue filter filtering audio sound signals of the at least oneITE microphone, and filter coefficients of the at least one cue filterfiltering audio sound signals of the at least one BTE microphone bysolving equation:$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{i}^{BTEC}{(f)}}}{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{H_{l,{ref}}^{ITEC}(f)} -} \\{{\sum\limits_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}}$ subject  to$\frac{1}{{{\sum_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} + {\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}}} \geq {{MSG}(f)}$wherein MSG(f) is a maximum stable gain, p is an integer, W(l) isangular weight(s), and W(ƒ) is frequency weight(s).
 19. The apparatusaccording to claim 16, wherein the transfer functions that includespatial cues comprise Head-Related Transfer functions HRTF_(l)(ƒ); andwherein the Head-Related Transfer functions HRTF_(l)(ƒ) are based on ahearing aid related transfer function H_(l,ref) ^(ITEC)(ƒ), and whereinthe processing unit is configured to determine filter coefficients ofthe at least one cue filter filtering audio sound signals of the atleast one ITE microphone, and filter coefficients of the at least onecue filter filtering audio sound signals of the at least one BTEmicrophone by solving equation:$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{j}^{BTEC}{(f)}}}\begin{pmatrix}{{\sum\limits_{l = 0}^{L - 1}{{W(l)}{{{W(f)}\begin{pmatrix}{{H_{l,{ref}}^{ITEC}(f)} -} \\{{\sum\limits_{i \neq {ref}}{G_{i}^{IEC}(f){H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}} +} \\{\alpha{{{\sum\limits_{i \neq {ref}}{{G_{i}^{IEC}(f)}{H_{{FB},i}^{IEC}(f)}}} + {\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{{FB},j}^{BTEC}(f)}}}}}^{p}}\end{pmatrix}$ wherein α is a weighting factor balancing spatial cueaccuracy and feedback performance, p is an integer, W(l) is angularweight(s), and W(ƒ) is frequency weight(s).
 20. The apparatus accordingto claim 15, wherein the transfer functions that include spatial cuescomprise Head-Related Transfer functions HRTF_(l)(ƒ); and wherein theprocessing unit is configured for determining the Head-Related Transferfunctions HRTF_(l)(ƒ), the hearing aid related transfer function H_(l,i)^(IEC)(ƒ), and the hearing aid related transfer functions HRTF_(l,i)^(BTEC)(ƒ) with the hearing aid mounted on an artificial head.
 21. Theapparatus according to claim 15, wherein the transfer functions thatinclude spatial cues comprise Head-Related Transfer functionsHRTF_(l)(ƒ) and wherein the processing unit is configured fordetermining the Head-Related Transfer functions HRTF_(l)(ƒ), the hearingaid related transfer function H_(l,i) ^(IEC)(ƒ), and the hearing aidrelated transfer functions H_(l,i) ^(BTEC)(ƒ) for a number of users; andwherein the processing unit is configured to determine filtercoefficients of the at least one cue filter filtering audio soundsignals of the at least one BTE microphone based on an average value ofthe Head-Related Transfer functions HRTF_(l)(ƒ), an average value of thehearing aid related transfer function H_(l,i) ^(ITEC)(ƒ), and an averagevalue of the hearing aid related transfer functions H_(l,i) ^(BTEC)(ƒ),of the number of users.
 22. The apparatus according to claim 15, whereinthe BTE hearing aid has a plurality of frequency channels; and whereinthe processing unit is configured for determining filter coefficients ofthe at least one cue filter filtering audio sound signals of the atleast one ITE microphone, and filter coefficients of the at least onecue filter filtering audio sound signals of the at least one BTEmicrophone, in one or more of the frequency channels.
 23. The apparatusaccording to claim 22, wherein the processing unit is further configuredfor disconnecting the at least one BTE microphone in one or more of thefrequency channels so that hearing loss compensation is performed solelyon an output of the at least one ITE microphone.
 24. The apparatusaccording to claim 15, wherein the processing unit is further configuredfor generating a hearing loss compensated output signal based on acombination of filtered audio sound signals output by the at least onecue filter filtering audio sound signals of the at least one ITEmicrophone, or by the at least one cue filter filtering audio soundsignals of the at least one BTE microphone, or by both.
 25. Theapparatus according to claim 15, wherein the transfer functions thatinclude spatial cues comprise Head-Related Transfer functionsHRTF_(l)(ƒ) and the minimization problem is based on the equation:$\min\limits_{{G_{i}^{IEC}{(f)}},{G_{i}^{BTEC}{(f)}}}{\overset{L - 1}{\sum\limits_{l = 0}}{{W(l)}{{{W(f)}\begin{pmatrix}{{{HRTF}_{l}(f)} -} \\{{\sum\limits_{i}{G_{i}^{IEC}(f){H_{l,i}^{IEC}(f)}}} -} \\{\sum\limits_{j}{{G_{j}^{BTEC}(f)}{H_{l,j}^{BTEC}(f)}}}\end{pmatrix}}}^{p}}}$ wherein W(l) is an angular weighting factor,W(ƒ) is a frequency dependent weighting factor, and p is a positiveinteger.
 26. The apparatus according to claim 25, wherein W(l)=1. 27.The apparatus according to claim 25, wherein W(ƒ)=1.
 28. The apparatusaccording to claim 25, wherein p=2.